Python for Linux System Administration


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Slides for "Python for Linux System Administration" given at Ohio Linux Fest, Columbus, OH, 09-26-2009

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Python for Linux System Administration

  1. 1. Python for Linux system administration (yes, this is a commercial) Vern Ceder Fort Wayne LUG Fort Wayne, IN
  2. 2. Instead of? the “official” languages for sysamins bash* (and awk and sed) *or your favorite similar shell perl (if you don't believe me, ask O'Reilly)
  3. 3.
  4. 4. A scripting language should handle input & output process text – search, replace, pattern matching, etc. traverse filesystems use system utilities and libraries (glue)
  5. 5. What's wrong with bash & perl? Nothing, really...
  6. 6. bash is a great glue language pipes things like a champ has a ton of utilities (the whole system, in fact)
  7. 7. awk and sed handle strings brilliantly
  8. 8. perl combines it all...
  9. 9. but... bash is a pain when things get complex sed is tricky perl makes my head hurt (I always have rather liked awk)
  10. 10. So what about Python? handles strings well is a good “glue” “batteries included” → I/O, filesystem, etc large collection of external libs
  11. 11. Python also is very readable (and easy to maintain) is expressive is easy to grasp is either OO (or not) is fun
  12. 12. everyone's doing it Redhat Ubuntu Google etc, etc, etc...
  13. 13. but... (there's always a “but”) regular expressions aren't built-in not (quite) as common as perl
  14. 14. and let's talk about the elephant in the room
  15. 15. indentation yes, Python uses indentation to organize code it makes code more readable it's no weirder than {} or @$% get over it
  16. 16. strings some built-in string methods split lower strip upper join isdigit replace swapcase find expandtabs count center startswith encode/decode endswith format
  17. 17. for example to do what wc does: #!/usr/bin/env python import sys data = chars = len(data) words = len(data.split()) lines = len(data.split('n')) print ("{0} {1} {2}".format(lines, words, chars)) doc@paladin:~/work/olf$ ./ < 12 22 189
  18. 18. or number of occurrences? in bash (not mine): doc@pal:~/olf$ tr " " "n" < | grep len | wc -w 3 in Python: #!/usr/bin/env python import sys data = print data.count(sys.argv[1]) doc@paladin:~/work/olf$ ./ len < 3
  19. 19. regular expressions re module syntax similar to perl import re >>> re.findall("[Ll]en", "len is the Length") ['len', 'Len']
  20. 20. exception handling y = 10 try: x = y / 0 except ZeroDivisionError, e: print e integer division or modulo by zero
  21. 21. glue multiple ways to call other programs and pipe the results sys.stdin, sys.stdout, sys.stderr os.system(), os.spawnl() subprocess.Popen()
  22. 22. Modules: subprocess from subprocess import * p = Popen(["ls", "-l"], stdout=PIPE, stderr=PIPE) out, err = p.communicate()
  23. 23. files, directories and more the os and sys modules os.environ sys.argv os.getcwd sys.stdin os.chmod sys.stdout os.chown sys.stderr sys.platform os.mkdir sys.exit os.remove os.rename
  24. 24. Modules: os os.walk() import os >>> for x in os.walk('.'): ... print x ... ('.', ['emptydir'], [ 'chinese-python- poster.jpg', 'olf_proposal.txt', '', 'olf.odp', 'shell.png', 'olf.txt', 'Pil.gif', 'adminscripting.png', '']) ('./emptydir', [], [])
  25. 25. Modules: os.path exists getmtime isfile isdir islink ismount samefile split
  26. 26. command line arguments sys.argv list of all arguments optparse parsing all types of arguments returns options and parameters automatic help
  27. 27. Modules: others databases – sqlite3 and others fork threading
  28. 28. ssh – paramiko #!/usr/bin/env python import paramiko hostname = 'localhost' port = 22 username = 'test' password = 'password' paramiko.util.log_to_file('paramiko.log') s = paramiko.SSHClient() s.load_system_host_keys() s.connect(hostname, port, username, password) stdin, stdout, stderr = s.exec_command('ifconfig') print s.close()
  29. 29. daemons python-daemon import daemon from spam import main_program with daemon.DaemonContext(): main_program
  30. 30. ctypes load and use C libraries also works with Windows DLL's >>> from ctypes import * >>> libc = CDLL("") >>> libc.printf("hello %sn", "Python") hello Python 13 >>> print libc.time(None) 1253757776 >>> import datetime >>> datetime.datetime.fromtimestamp(libc.time(None)) datetime.datetime(2009, 9, 23, 22, 5, 56)
  31. 31. A 2 line HTTP server from http.server import HTTPServer, SimpleHTTPRequestHandler server = HTTPServer(("",8000), SimpleHTTPRequestHandler) server.serve_forever()
  32. 32. What about Python 3? it's a better language than 2.x it's not backward compatible it's supported by the developers it's the future it's not here (for sysadmins) yet
  33. 33. ipython, the uber shell extensive history usable as a system shell In [1]: print "hello" ------> print("hello") hello In [2]: ls adminscripting.png olf.odp Pil.gif
  34. 34. nd Quick Python Book, 2 ed covering Python 3 due out late this year
  35. 35. World's largest Python conference Talks PyCon 2010 Open Space Tutorials Hands-On Lab Lightning Talks Feb. 17-25 Exhibit Hall Keynotes Atlanta, GA Sprints NOW with Poster sessions! Photo: james.rintamaki License: Attribution- Share Alike 2.0 Generic
  36. 36. Resources & contact info Python for Unix and Linux System Administration, Noah Gift, Jeremy M. Jones, O'Reilly Media 2008 Pro Python System Administration, Rytis Sileika, Apress, (not yet published) “Python for system administrators”, James Knowlton, IBM DeveloperWorks, 2007 Python Cookbook, Martelli, Ravenscroft & Ascher, O'Reilly Media 2005
  37. 37. Contact info